Default Calendar // Help in tweaking the dateheaders mode

When I’m in dateheaders mode, the fulldayevents are always displayed on the start date.

I would like it to be displayed starting today’s date even if the fulldayevent started days before.

i.e : I’ve a fulldayevent which started on March 6th and finishes tomorrow.
In the dateheaders view, event is displayed on March 6th date. Which I don’t want.
What I would like is to see it in today’s + tomorrow’s header.

I’ve already tried to modify calendar.js line 258 in several ways but don’t manage to get it done. (maybe it’s even not the right line to modify…)